fix undo after mm rest change
fix crash when dropping fretdiagram on frame
fix some crash with invalid drumset
merge README into README.md
fix #22911: slur entry broken
fix mtest reference
fix #22769 : staff or system text over more lines
Merge pull request #496 from AntonioBL/simpletext_lines

fix #22769 : staff or system text over more lines
Merge remote-tracking branch 'origin/master' into Working-Branch